When did Dexter break Harry's code for the first time?

But, when did he break it for the first time?

At first thought, Dexter started breaking the code (quite frequently) once he got involved with Rita.

Before Rita, Dexter didn't really have any distractions, and he followed Harry's code completely. Once Dexter started dating Rita though (even as a cover), he began realizing that Harry might not have been right about everything, and that he perhaps misjudged some aspects of Dexter (but really, perhaps not).

Harry would often say that Dexter has too much on his plate by juggling work, a girlfriend, being a brother to Deb, and being an uncaught (and for a while undetected) serial killer. Once Dexter realized that it might actually be possible for him to be "normal", and to have people that depend on and care about him (i.e., Rita and the kids, not just Deb), he goes against Harry's code and starts paving his own way. This desire to feel needed and important to others is something that Dexter speaks about on several accounts, especially during the Arthur Mitchell timeline (season 4).

Dexter's progressive rebellion of Harry's teachings (in some aspects, not everything), over time, eventually compounds into him questioning nearly everything about Harry and the code. This leads Dexter to abandoning the code all together at certain times, seen most extremely in S05E01 (during the bathroom killing).

@Charles Time period/episode...

Dexter meets and starts dating Rita during the Ice Truck Killer manhunt.. so, maybe episode 6 or 7 of season 1?